The invention relates to a nodular cast iron alloy for cast iron products having a high modulus of elasticity, the nodular cast iron alloy containing, as nonferrous constituents, at least the elements C, Si, Mn, Cu, Mg, S and, as admixtures, Ni and/or Mo.
Nodular cast iron alloys are used in the automotive industry for the production of castings which have to have a high resistance to torsional moments, for example the crankshaft, as part of the engine in the motor vehicle. The castings often have a very complex geometry with numerous areas which are subject to different levels of load and therefore have different wall thicknesses. This requires a casting technique which is suitable for parts with greatly differentiated geometries. Also, the castings often have to be aftertreated. The after treatment may be a heat treatment and/or a machining treatment. An important property which is desired for castings of this type is a modulus of elasticity which is as high as possible. Alloys with a modulus of elasticity of up to approximately 160 GPa are currently customary. A steel alloy will usually be used for parts with a modulus of elasticity which is as high as possible, and the parts will then be worked by forging. However, this is an expensive production method.
WO 99/19525 has disclosed a nodular cast iron alloy which can be used for shafts and disks of a disk brake. In per cent by weight, the alloy contains 1.5 to 4.5% of C, 1.5 to 4.5% of Si and at least 1.0 to 6.5% of Mo, as well as if appropriate Ni and Cu, the sum (% of Mo+% of Ni+% of Cu) not exceeding 6.5%, remainder iron and standard impurities. The alloy is distinguished by a good resistance to high temperatures and abrasion.
WO 96/38596 has disclosed a nodular cast iron alloy with a high modulus of elasticity.
The alloy contains, in per cent by weight: 3.0 to 3.8% of C, 2.0 to 2.6% of Si, 0.2 to 0.6% of manganese, less than 0.02% of P, less than 0.03% of S, 0.03 to 0.06% of magnesium, 0.8 to 1.2% of Ni, 0.8 to 1.2% of Cu, 0.4 to 1.0% of Mo, remainder Fe.
Nodular cast iron alloys with high pearlite and graphite contents are known. In these known alloys, the modulus of elasticity is too low for certain applications. If the graphite content is kept at a low level, the matrix content increases, as does the modulus of elasticity. More solid solution than graphite is formed.
Working on the basis of this prior art, it is an object of the invention to provide a nodular cast iron alloy for cast iron products with a modulus of elasticity of higher than 170 GPa.